Associate Professor
Geosphere and Biosphere Science Group

Office: Science Bldg. #1-534
TEL: +81-3-5841-4522
FAX: --

Research Field

Paleontology, Evolutionary Developmental Biology

Current Research

The fossil record empirically shows heterogeneous patterns of morphological diversification in evolution: morphological evolution has seen arrested and rapid phases in the past. In other words, evolutionary rates and diversity in morphology have not been homogeneous in geological time scale, and "evolvability" appears to vary by phylogenetic position. Such evolutionary patterns must be governed both by adaptation (external factor) and by developmental constraints, or limitations of directions and ranges in evolutionary change caused by characteristics of developmental systems (internal factor). However, the conventional paleontological studies have focused only on the external factor, and it remains unclear how the developmental constraints have affected the evolutionary pattern. On the other hand, in evolutionary developmental biology (evo-devo), scientists have not paid attention to extinctions, which act as evolutionary "pruning." In particular, possibilities that mass extinction produced the bases for developmental constraints and that specific lineages rapidly diversified after mass extinctions possessed more "evolvable" characteristics of developmental systems than those of other lineages are open questions.
To solve these problems, as well as understanding of the relationship between the evolution and the external factor including global environmental changes, clarification of developmental constraints through comparative analyses of embryonic developments and experiments artificially altering developmental processes are essential. The latter will lead to a bridge between paleontology and genomics, and also to predictions of future biodiversity. I am pioneering a new interdisciplinary research field focusing on both
external and internal factors, with the following subjects:
(1) Evolution of skeletal muscles, in particular limb muscles, of vertebrates
(2) Evolution of respiratory systems of vertebrates
(3) Anatomical reconstructions of fossil taxa based on comparative morphology
My laboratory utilizes detailed analyses of fossil specimens (e.g., synchrotron radiation X-ray microCT), as well as developmental genetic analyses at gene and cellular levels. Also, fieldworks are important for collecting data about evolutionary patterns. The projects involve international collaborations.

Representative Publications

1. Hirasawa T., et al. (2022) Morphology of Palaeospondylus shows affinity to tetrapod ancestors. Nature, 606: 109–112.
2. Hirasawa T. and Kuratani S. (2018) Evolution of the muscular system in tetrapod limbs. Zoological Letters, 4: 27.
3. Hirasawa T., Nagashima H. and Kuratani S. (2013) The endoskeletal origin of the turtle carapace. Nature Communications, 4: 2107.